Bushing device for introducing current conductor into compressed gas switch chambers



March 22, 1966 D. FLOESSEL ,251

BUSHING DEVICE FOR INTRODUCING CURRENT CONDUCTOR INTO COMPRESSED GAS SWITCH CHAMBERS 2 Sheets-Sheet 1 Filed July 3, 1965 INVENTOR. D/efer F/oesseL BY lie-Mp I III, M

March 22, 1966 D. FLOESSEL 3,242,251

I BUSHING DEVICE FOR INTRODUCING CURRENT CONDUCTOR INTO COMPRESSED GAS SWITCH CHAMBERS Filed July 5, 1963 2 Sheets-Sheet-2 iqos q- CI INVENTOR. DLeier FloesseL 3,242,251 U H NG DEVICE FOR INTRODUCING CURRENT CONDUCTOR INTO COMPRESSED GAS SWITCH CHAMBERS DieterFloessel, Fislisbac'h, Switzerland, assignor to Aktiengesellschaft Brown, Boveri '& Cie., Baden, Switzerland, a joint-stock company I Filed July 3, 1963, Ser. No. 292,543

Claims priority, ap lication Switzerland, July 10, 1962,

8,294/62; Dec. 20, 1962, 14,922/62 Claims. (Cl'. 174-18) The present invention refers to an electrical bushing in particular for the introducing of current into the interr'upter-chamber of a gas-pressure circuit breaker. In circuit breakers whose interrupter-chambers comprise of a metallic housing filled with gas under pressure, in which the interrupter-contacts are located whereby the movable contact is electrically connected to the metallic housing and the stationary contact is carried by a con ductor, said conductor must be led into the housing of the interrupter-chamber in such a way that it is insulated from the housing. To achieve this, the conductor is contained within a hollow insulator and the combination of conductor and insulator constitutes a bushing. It is common practice'to provide the bushing insulator with fittings cemented to it.- These fittings are so con structed as to act at one end as a flange for the purpose of fixing the bushing to the housing while at the other end the flange serves as the terminal cap of the bushing. This method has the disadvantage that the hollow insulator is subjected to both bending and tension stresses which result both from'the external forces due to terr'ninal conductors and from the filling of gas under pressure.

The fittings mounted on the insulator necessitate also an increase in height of the insulator if a definite length of creepage path or a definite gap length between metal parts is prescribed. i g

The invention has the purpose, among others, of providing an arrangement for a bushing in which "the 1161 low insulator is subjected to compressive stresses only, while the height of the bushing is reduced to a minimum.

.It is therefore proposed, according to the invention, that the bushing consist of at least one hollow insulator and one insulating tension-tube, which is contained within the hollow insulator and which surrounds the'eondu'ctor' at least in part, and that elastic means be provided through which the tension-tube is connected to both the fixing and terminal flanges; By means of this arrangement, a favorable stressing of the hollow insulator is: achieved and at the same time. it is made possible, in an advantageous manner, to compensate for possible changes in length resulting, for example, from expansions due to heating or elastic yielding of the various parts.

The accompanying drawings show two embodiments by which this objective is obtained and the invention will he explained with reference to these drawings.

RIG. 1 shows, partly in section, a. bushing according to the invention.

FIG. 2 shows a further example of construction.

In FIG. 1, the conductor is designated with 1 and extends through a longitudinal bore in. the insulator 2. The latter is connected on its upper end to a flange 3 which in turn, is rigidly connected to -a housing 4 of the interrupter-chamber. The flange 3 carries a tapered shoulder 3a on its inside surface to support the insulating.

tension-tube 5 which has a corresponding tapered shoulder 5a on its upper end engaging shoulder 3a. According to the invention, the tension-tube 5 is made of a high-strength insulating material with fibre-reinforcement. On its lower end the tension-tube 5 has a further tapered 3,242,251 Patented Mar. 22, 1966 shoulder 5b which is a corresponding tapered shoulder 6a on the tension-sleeve 6. The tension-sleeve 6 is rigidly connected to the conductor 1 by means of a cross pin 7. Sleeve 6 is fitted with a screw thread to engage the nut 8. Then tensile forces produced by the tightening of the nut 8 are transmitted through anend-cap 9, disc 10 and disc springs 11 to an annular fitting member 12 which surrounds the sleeve 6 and which is capable of axial movement with respect to said sleeve. In this way, the hollow insulator 2 is stressed, solely by compressive forces, between the parts 3 and 12 by reason of the tension-tube 5 being subjected to tensile stresses. This is of particular advantage if the insulator 2 is made of ceramic material because, as is well known, this material permits a much higher stressing by compressive forces than by tensile forces. The disc springs ll serve to compensate possible changes in length arising from various expansions of the conductor caused by heating or cooling while in operation. A tapered insulating sleeve 13 is provided as a strut for the conductor 1 within the tension-tube 5. To prevent axial movement, the insulating sleeve 13 is rigidly joined to the tension-tube 5 at position 14 by means of an adhesive connection. By reason of the tapered shape of sleeve 13 a large creepage path is provided between flange 3 and the conductor 1. A cylindrical electrode 15 of conducting material, which serves to control the electric field, is inserted in the flange 3 between insulator 2 and tension-tube 5 and, in the usual manner, as a projecting electrode, relieves the region in which the flange 3 and the conductor 1 are close together at the entrance to the housing 4 of the interrupter-cham ber. By means of axially extending channels 16 in the insulating sleeve 13, the housing 4, which is filled with gas under pressure, is connected to the inside of the hollow insulator 2. To provide for the case when the filling of the interrupter-chamber with gas under pressure is carried out through the bushing, the flange 12 is providedwith a connecting nipple 17 while the sleeve 6 is provided with an opening 18 and axially extending cavities 19, by means of which the gas flows through the H bushing into the interrupter chamber. The intermediate layer of material 20 ensures that the nut 8 is not tightened too rigidly.

For the case Where the internal pressure in the bushing is relatively high, e.g. 2O atmospheres, which arises, for example, with gas-pressure circuit breakers, the, disc springs 11 must be designed for a fairly large compressive force in order to ensure that the sealing between the bearing surfaces of the hollow insulator and the end flanges is always maintained even when the above mentioned changes in length occur.

Further advantage may be gained within the scope of the invention it the greater part of the stressing forces and hence, the sealing force is brought about by the gas pressure existing Within the bushing. The disc springs 11 may then be designed essentially weaker because they would only need to maintain the sealing during the time when the bushing is not under internal gas-pressure. The hollow. insulator is then closed at its lower end by an annular in cylinder in which a movable piston, secured to the conductor, is situated. While the piston is capable of movement within its cylinder it nevertheless maintains a seal, and the cylinder exerts an additional force on the hollow insulator because of the gas pressure existing in the bushing.

FIG. 2 shows an arrangement of such a bushing in section. The conductor 101 is connected through. the insulating tube 105, which is provided with tapered shoulders, to the housing 103 of the interrupter-chamber. The tension-tube is surrounded concentrically by the hollow insulator 102 which in turn is in contact at its upper end surface with the housing 103 and at its lower end surface with an annular cylinder 104. In order to achieve a seal between the hollow insulator 102 and the parts 103 and 104 respectively, sealing rings 109 are provided which lie in the usual circular slots. In the cylinder 104 the piston 106 is supported in a sliding air-tight manner and is held rigidly against a collar 101b by means of the nut 107. This collar 101b is a bell-shaped widening of the conductor 101. The pre-stressed disc springs 108 act in the space between the piston 106 and cylinder 104. The space between the tension-tube 105 and the hollow insulator 102 is always connected to the space within the interrupter-chamber of the breaker through the opening 110 in the housing 103. For external connections, the conductor 101 is fitted On its lower end with a terminal bolt 101a.

The arrangement as shown in FIG. 2 operates so that when the bushing is not under internal pressure, the forces on the hollow insulator 102 are brought about by the pre-stressed disc springs 108. If the interrupterchamber and hence, also the bushing is now filled with pressurized gas, the pressure between the parts 102 and 103 and between the parts 102 and 104 increases with increase in gas-pressure because now a force, given by the product of the gas-pressure and the effective annular area a, is produced. This force is maintained even when unequal expansions due to heating take place in the parts 102 and 105 during service because the piston 106, which is rigidly connected to the conductor 101, isfree to move axially within cylinder 104. In this way the hollow insulator 102 may be made of porcelain and the tensiontube 105 may be made of polyester i.e. materials which have vastly different coefficients of expansion, without adversely affecting the sealing of the bushing. I

The scope of the invention is, of course, not limited to the examples shown. The hollow insulator may, for example, consist of several parts which are axially pressed together in the same way by means of a tension-tube whereby circular intermediate plates are arranged between the individual constituent pieces. A further advantage of the new arrangement is that in the event of possible internal over-pressures, such as those arising from disturbances in the interrupter-chamben an explosive bursting of the hollow insulator is avoided by reason maggot the protective tension-tube and also only a' small volume of gas exists between tension-tube sulator.

I claim: V

1. In an electrical circuit breaker, the combination comprising a gas-filled metallic housing within which the circuit breaker contacts are located, said housing including an opening through which a rigid conductor rod passes to the exterior of the housing from one of said con tact members, and a bushing structure surrounding said conductor rod exteriorly of said housing for insulating said conductor rod from said housing, said bushing structure comprising an outer hollow ceramic insulator surrounding said conductorrod and having one end thereof bearing against said housing adjacent said opening, a tension tube of insulating material surrounding said conductor rod and located in the annular space between said conductor rod and ceramic insulator, means adjacent said housing opening for securing the corresponding end of said tension tube against movement, a metallic tension sleeve secured to said conductor rod adjacent the opposite end of said ceramic insulator, means securing the other end of said tension tube to said tension sleeve, a tightening nut'threaded onto a threaded portion of said tension sleeve, an annulan fitting member carried by and surrounding said tension sleeve, said fitting member being and hollow inin contact with said opposite end of said ceramic insulator and movable axially on said tension sleeve, and spring means surrounding said tensionsleeve and located intermediate said nut and said fitting member for resiliently exerting a compressive force on said ceramic insulator,

said force being transmitted from said nut through said spring means and said fitting member accompanied by a corresponding reactive force in tension exerted on said tension tube.

2. The invention as defined in claim 1 wherein said tension sleeve includes an opening through the wall thereof and said annular fitting member also includes an open ing through the wall thereof for admitting a pressurized gas into said metallic housing through said bushing structure.

3. The invention as defined in claim 1 and which further includes a tapered tubular insulating member located in the space between said conductor rod and tension tube, opposite ends of said tapered insulating member being in contact with said conductor rod and tension tube respectively for supporting said conductor rod within said tension tube.

4. In an electrical circuit breaker, the combination comprising a gas-filled metallic housing within which the circuit breaker contacts are located, said housing including an opening through which a rigid conductor rod passes to the exterior of the housing from one of said contact members, and a bushing structure surrounding said conductor rod exteriorly of said housing for insulating said conductor rod from said housing, said bushing structure comprising an outer hollow ceramic insulator surrounding said conductor rod and having one end thereof bearing against said housing adjacent said opening, a tension tube of insulating material surrounding said conductor rod and located in the annular space between said conductor rod and ceramic insulator, means adjacent said housing opening for securing the corresponding end of said tension tube against movement, means securing the the other end of said tension tube to said conductor rod, an annular cylinder surrounding said tension tube and in contact with said opposite end of said ceramic insulator, an annular piston slidable within said annular cylinder, means securing said piston to said conductorrod, and spring means located in said annular cylinder be tween said piston and the cylinder end in contact with said ceramic insulator for applying a' resilient compressive force to said ceramic cylinder and which is accompanied by a corresponding reactive force in tension exerted on said tension tube.

5. The invention as defined in claim 4 and which fur-. ther includes means for placing that portion of the in terior of said annular cylinder adjacent the cylinder end in contact with said opposite end of said ceramic insulator in communication-with the pressure gas filled interior of said circuit breaker housing whereby said gas pressure establishes an additional compressive force on said ceramic insulator.

References Cited by the Examiner UNITED STATES PATENTS 1,770,130 7/1930 Dunmire 174-30 2,534,920 12/1950 Ludwig et a1. 200- 2,930,841 3/1960 Johnston et al. 174-31 X 3,178,505 4/1965 VanSickle 174--l42 X FOREIGN PATENTS 512,217 4/1955 Canada. 218,749 4/ 1942 Switzerland.

JOHN F. BURNS, Primary Examiner. LARAMIE ASKIN, Examiner. 

1. IN AN ELECTRICAL CIRCUIT BREAKER, THE COMBINATION COMPRISING A GAS-FILLED METALLIC HOUSING WITHIN WHICH THE CIRCUIT BREAKER CONTACTS ARE LOCATED, SAID HOUSING INCLUDING AN OPENING THROUGH WHICH A RIGID CONDUCTOR ROD PASSES TO THE EXTERIOR OF THE HOUSING FROM ONE OF SAID CONTACT MEMBERS, AND A BUSHING STRUCTURE SURROUNDING SAID CONDUCTOR ROD EXTERIORLY OF SAID HOUSING FOR INSULATING SAID CONDUCTOR ROD FROM SAID HOUSING, SAID BUSHING STRUCTURE COMPRISING AN OUTER HOLLOW CERAMIC INSULATOR SURROUNDING SAID CONDUCTOR ROD AND HAVING ONE END THEREOF BEARING AGAINST SAID HOUSING ADJACENT SAID OPENING, A TENSION TUBE OF INSULATING MATERIAL SURROUNDING SAID CONDUCTOR ROD AND LOCATED IN THE ANNULAR SPACE BETWEEN SAID CONDUCTOR ROD AND CERAMIC INSULATOR, MEANS ADJACENT SAID HOUSING OPENING FOR SECURING THE CORRESPONDING END OF SAID TENSION TUBE AGAINST MOVEMENT, A METALLIC TENSION SLEEVE SECURED TO SAID CONDUCTOR ROD ADJACENT THE OPPOSITE END OF SAID CERAMIC INSULATOR, MEANS SECURING THE OTHER END OF SAID TENSION TUBE TO SAID TENSION SLEEVE, A TIGHTENING NUT THREADED ONTO A THREADED PORTION OF SAID TENSION SLEEVE, AN ANNULAR FITTING MEMBER CARRIED BY AND SURROUNDING SAID TENSION SLEEVE, SAID FITTING MEMBER BEING IN CONTACT WITH SAID OPPOSITE END OF SAID CERAMIC INSULATOR AND MOVABLE AXIALLY ON SAID TENSION SLEEVE, AND SPRING MEANS SURROUNDING SAID TENSION SLEEVE AND LOCATED INTERMEDIATE SAID NUT AND SAID FITTING MEMBER FOR RESILIENTLY EXERTING A COMPRESSIVE FORCE ON SAID CERAMIC INSULATOR, SAID FORCE BEING TRANSMITTED FROM SAID NUT THROUGH SAID SPRING MEANS AND SAID FITTING MEMBER ACCOMPANIED BY A CORRESPONDING REACTIVE FORCE IN TENSION EXERTED ON SAID TENSION TUBE. 